These studies are directed towards improved understanding and therapeutic approaches to neonatal septicemia, a significant cause of child mortality. The studies are specifically directed towards further understanding of the neonatal inflammatory response, particularly the process of phagocytosis, chemotaxis and random mobility, and leukocyte deformability. Two main groups of experiments are involved. The first involves studies of the cellular components of these processes. Leukocytes from normal neonates and from patients with previously described abnormalities of chemotaxis and random mobility will be utilized. The second group of studies involves further inquiries into the role of complement, particularly the fifth component (C5) in phagocytosis. They are based upon previous demonstrations from this laboratory of a human deficiency state of C5 and deficient C5 activity in yeast phagocytosis in neonatal sera. A further aim of the studies is to increase understanding of the previously identified deficiencies of the inflammatory response and examine new therapeutic approaches to them.